The present invention relates to a DC linear voltage regulator circuit for generating a regulated DC output voltage based on a DC input voltage. The DC linear voltage regulator circuit comprises a switchable leakage prevention circuit configured to automatically detect and interrupt a flow of leakage current from the regulator output to the bulk terminal of a DMOS pass transistor of the regulator. Certain types of applications of DMOS based DC linear voltage regulators require that an external DC voltage source can be applied to a regulator output under operating conditions where the DC voltage at the regulator input, i.e. the supply voltage of the DC linear regulator circuit, is zero or much smaller than the DC voltage forced onto the regulator output. Applying this type of reverse voltage operating conditions to prior art DMOS based DC linear voltage regulators will often result in a huge and unacceptable reverse leakage current flowing from the regulator output into the DMOS pass transistor. This imparts and serious waste of power in the DC linear voltage regulator circuit under reverse operation conditions and may additionally damage various active and passive components the DC linear voltage regulator by overheating. There are at least two mechanisms that cause this undesired reverse flow of leakage current. A large portion of the leakage current is flowing through the bulk of the DMOS pass transistor device because the bulk is connected to the regulator input which is connected to the DC input voltage during normal operation of the DC linear voltage regulator. In addition another portion of the leakage current may be flowing through the channel of the DMOS pass transistor because an output of the driver or error amplifier for the DMOS pass transistor and a Zener protection diode on a gate terminal of the DMOS pass transistor grounds the gate terminal when the DC input voltage is zero. Even though the DMOS is asymmetric between drain and source there may be formed a channel in the DMOS pass transistor supporting a substantial reverse current flow.
Hence, it will be advantageous to provide a of DMOS based DC linear voltage regulator circuit that can withstand the above-mentioned reverse operating conditions without suffering from a huge flow of reverse leakage current from the external DC voltage source coupled to the regulator output and into the DMOS pass transistor.